Plato: [Rhetoric] is
the "art of enchanting the soul." (The art of winning the soul by discourse.)

Aristotle:
Rhetoric is "the faculty of discovering in any particular case all of the
available means of persuasion."

Cicero:
"Rhetoric is one great art comprised of five lesser arts: inventio,
dispositio, elocutio, memoria, and pronunciatio." Rhetoric is "speech
designed to persuade."

Quintilian:
"Rhetoric is the art of speaking well" or "...good man speaking
well."

Francis Bacon: The duty and office of
rhetoric is to apply reason to imagination for the better moving of the
will.

George Campbell:
"[Rhetoric] is that art or talent by which discourse is adapted to
its end. The four ends of discourse are to enlighten the understanding,
please the imagination, move the passion, and influence the will."

Henry Ward Beecher:
“Not until human nature is other than what it is, will the function of
the living voice-the greatest force on earth among men-cease...I
advocate, therefore, in its full extent, and for every reason of
humanity, of patriotism, and of religion, a more thorough culture of
oratory and I define oratory to be the art of influencing conduct with
the truth set home by all the resources of the living man.”

I. A. Richards:
Rhetoric is the study of misunderstandings and their remedies.

Richard Weaver:
Rhetoric is that "which creates an informed appetition for the
good."

Erika Lindemann:
"Rhetoric is a form of reasoning about probabilities, based on
assumptions people share as members of a community."

Philip Johnson:
"Rhetoric is the art of framing an argument so that it can be
appreciated by an audience."

Andrea Lunsford:
"Rhetoric is the art, practice, and study of human communication."

Kenneth Burke: "The most
characteristic concern of rhetoric [is] the manipulation of men's beliefs
for political ends....the basic function of rhetoric [is] the use of words
by human agents to form attitudes or to induce actions in other human
agents."

George Kennedy: Rhetoric in the most
general sense may perhaps be identified with the energy inherent in
communication: the emotional energy that impels the speaker to speak, the
physical energy expanded in the utterance, the energy level coded in the
message, and the energy experienced by the recipient in decoding the
message.

Lloyd Bitzer: "...rhetoric is a mode of
altering reality, not by the direct application of energy to objects, but
by the creation of discourse which changes reality through the mediation
of thought and action."

Douglas Ehninger: "[Rhetoric is]
that discipline which studies all of the ways in which men may influence
each other's thinking and behavior through the strategic use of symbols."

Gerard A. Hauser: "Rhetoric is an
instrumental use of language. One person engages another person in an
exchange of symbols to accomplish some goal. It is not communication for
communication's sake. Rhetoric is communication that attempts to
coordinate social action. For this reason, rhetorical communication is
explicitly pragmatic. Its goal is to influence human choices on specific
matters that require immediate attention."

C. H. Knoblauch: "...rhetoric is the
process of using language to organize experience and communicate it to
others. It is also the study of how people use language to organize and
communicate experience. The word denotes both distinctive human activity
and the "science" concerned with understanding that activity."

John Locke: "[Rhetoric,] that powerful
instrument of error and deceit."

Charles Bazerman: "The study of
how people use language and other symbols to realize human goals and carry
out human activities...ultimately a practical study offering people
great control over their symbolic activity."

Michael Hyde and Craig Smith:
"The primordial function of rhetoric is to 'make-known' meaning both to
oneself and to others. Meaning is derived by a human being in and through
the interpretive understanding of reality. Rhetoric is the process of
making known that meaning. Is not rhetoric defined as pragmatic
communication, more concerned with the contemporary audiences and specific
questions than with universal audiences and general questions?"

Alfred North
Whitehead: "The
creation of the world -- said Plato -- is the victory of persuasion over
force. The worth of men consists in their liability to persuasion."

Samuel M. Edelman: "Rhetoric can be defined as the art or method of
reconciling...individual and systemic goals and constraints." (JCR Sept
2003)

Andrew King and Jim Kuypers: "The strategic use of communication,
oral or written, to achieve specifiable goals." (The Art of
Rhetorical Criticism, 2004)

Thomas B. Farrell: Rhetoric is an acquired competency, a manner of
thinking that invents possibilities for persuasion, conviction, action,
and judgments." (The Norms of Rhetorical Culture, 1993)

Richard E. Vatz:
"This [is the] sine qua non of rhetoric:
the art of linguistically or symbolically creating salience. After
salience is created, the situation must be translated into meaning.“(Philosophy and Rhetoric, 1973)

Michael E. Eidenmuller: "Rhetoric is a
rational study and artful practice of human symbol use (especially if
not exclusively with words) when and where those symbols target
identifiable communities of interest to create, enhance, undermine, or
otherwise influence human belief, attitude, emotion, judgment,
behavior." (Voice of America Interview, 2011, and modified
for print)